JPH0513547B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor device using quantum wells made of thin films having different compositions.

[Conventional technology]

Optical communication using fiber optic cables as a medium has the advantage of dramatically increasing communication capacity compared to conventional telecommunications using electric wire cables as a medium. With advances in communication technology and semiconductor manufacturing technology, optical communication has attracted attention and is expected to play a central role in future information communication. In particular, in optical communications, the development of various devices used for transmission of optical signals, selective arithmetic processing of optical signals, conversion with electrical signals, etc. has become an important issue, and research and development thereof are actively being carried out.

By the way, as a device for selective calculation processing of optical signals, it is desired that an optical bistable element whose output forms a hysteresis loop in response to changes in the intensity of incident light will emerge, and research is being actively conducted to realize this. is being carried out. In particular, this optical bistable element can produce a large change in output even with a small amount of incident light, can also produce a large output, and even if the input changes at high speed, the output can follow it and respond quickly.
It is desired that an element with good responsiveness such as sensitivity and response speed be developed.

[Problem that the invention seeks to solve]

However, conventional optical bistable devices whose output draws a hysteresis loop in response to changes in the intensity of incident light, such as those that do not use electrical elements or those that combine quantum wells and resistors, Although some devices have been developed, they have various problems in terms of performance and ease of use, such as low output power and poor response, and there are still no devices that are satisfactory for processing optical signals. The current situation is that it has not been developed.

The present invention is based on the above considerations, and includes:
The object of the present invention is to provide a semiconductor device using a quantum well that can realize an optical bistable device with excellent sensitivity and good response.

[Means for solving problems]

To this end, the semiconductor device using the quantum well of the present invention has a quantum well light control layer that is made of thin films with different compositions and whose light absorption characteristics shift from a high absorption coefficient to a low absorption coefficient in a specific wavelength region, and a It is characterized by applying a voltage to a non-linear resistance element having resistance characteristics in series, and controlling the input/output characteristics of light in the above-mentioned specific wavelength range in the light control layer. It is characterized by realizing a non-linear resistance element using the resonant tunneling effect in a plurality of quantum wells made of thin films and having different film thicknesses.

[Effect]

In the semiconductor device using the quantum well of the present invention, since the quantum well and the nonlinear resistance element are connected in series and a voltage is applied, the light absorption characteristic of the quantum well shifts from the absorption region to the transmission region in a specific wavelength range at the boundary. When light is input, the voltage sharing between the quantum well and the nonlinear resistance element changes depending on the intensity of the input light.
The quantum well transitions from absorption to transmission or from transmission to absorption. In other words, in a quantum well, the transition point between the absorption region and the transmission region shifts depending on the voltage (electric field strength) at both ends, and by connecting nonlinear resistance elements in series, the voltage at both ends can be adjusted to the intensity of the incident light. It changes depending on the situation. Further, by using the resonant tunneling effect in a plurality of quantum wells having different film thicknesses, it is possible to obtain an excellent nonlinear resistance element with a large resistance change.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 1 is a diagram for explaining one embodiment of a semiconductor device using a quantum well according to the present invention, FIG. 2 is a diagram showing light absorption characteristics of a quantum well, and FIG. 3 is a diagram showing a voltage difference of a nonlinear resistance element. FIG. 4 is a diagram showing the current characteristics, and FIG. 4 is a diagram showing the input/output characteristics of the optical bistable element.

In Figure 1, 1 is a power supply, 2 and 3 are thin films, and 4
indicates a non-linear resistance element. As shown in FIG. 1, the structure of the quantum well used in the present invention is, for example, a multiple quantum well in which a thin film 2 is sandwiched between thin films 3 having a different composition. This quantum well has absorption characteristics for incident light as shown in FIG. 2, and has a high absorption coefficient for light below a certain wavelength. The wavelength of this boundary is, for example, the wavelength of the thin film 2 constituting the quantum well.
When using GaAs, thin film 3 and AlGaAs
About 8000Å, and InGaAs for thin film 3, and InGaAs for thin film 3.
When InAlAs is used, it is approximately 1.5 μ (micron), and the wavelength of the boundary can be selected depending on the material. Further, the wavelength at this boundary has a characteristic that when a voltage is applied, it shifts to the longer wavelength side (from the solid line to the dotted line in FIG. 2). Therefore, the absorption properties can be changed by controlling the voltage. At a particular wavelength, for example λ _i shown in FIG. 2, it is possible to switch between a state with a high absorption coefficient and a state with a low absorption coefficient.

The optical bistable device according to the present invention utilizes this quantum well as a principle, as shown in the configuration shown in FIG. In addition to incorporating it into the junction, by connecting a non-linear resistance element 4 with negative resistance characteristics to it, connecting the power supply 1 to both ends, and applying a constant voltage _V3 , hysteresis characteristics can be created by the interaction of these elements. It was designed to bring about this. Here, the direction of the incident light may be perpendicular to the quantum well as shown, but it may also be horizontal. Alternatively, it may be a single-layer quantum well.

Next, the operation of the optical bistable device shown in FIG. 1 will be explained. First, to explain the properties of a quantum well, in a quantum well, almost no current flows when there is no incident light, but when there is incident light, a current flows according to the absorption of light, and therefore the intensity of the incident light increases. and varies depending on the wavelength. In other words, in the absorption characteristics shown in Figure 2, for light with a wavelength in the absorption region, a current flows by the amount of absorbed light, and for light with a long wavelength outside the absorption region, In this case, the current changes only slightly even if the incident light increases or decreases.

On the other hand, the nonlinear resistance element has the voltage-current characteristics shown in FIG. 3, as is well known. That is, the current increases in proportion to the voltage up to a certain voltage (point b in the figure), but beyond point b in the figure, the resistance rapidly increases and the current decreases in inverse proportion to the voltage.

Therefore, a quantum well light control layer and a non-linear resistance element having the above properties were connected in series as shown in Figure 1, and a constant voltage _V3 was applied to obtain the absorption characteristics shown in Figure 2. When wavelength λ _i is applied as incident light to a quantum well, the relationship between the incident light and output light shown in FIG. 4 is obtained. First, when the incident light is almost zero, the quantum well is in a high resistance state and no current flows. At this time, the voltage V ₁ of the quantum well becomes approximately the power supply voltage V ₃ , and the voltage V ₂ of the nonlinear resistance element becomes 0. Further, the absorption characteristics of the quantum well in this state are as shown by the dotted line in FIG. 2 because the voltage V ₁ is high.

Next, as the amount of incident light increases, since the quantum well has a high absorption coefficient, the incident light is absorbed, the current increases, and the voltage V ₂ of the nonlinear resistance element also increases. This process (a shown in Figures 3 and 4)
→ In b), even if the incident light increases, the output light remains close to 0 due to light absorption in the quantum well.

However, when the incident light increases further and the voltage V ₂ of the nonlinear resistance element exceeds point b shown in Figure 3, the resistance of the nonlinear resistance element increases rapidly, and the current decreases, but the nonlinear resistance element The voltage V ₂ transitions to a high point (b→d shown in FIGS. 3 and 4).
Therefore, the voltage V ₁ of the quantum well decreases rapidly, and the absorption characteristic shifts from the dotted line to the solid line in FIG. 2.
Therefore, absorption in the quantum well disappears at this point, most of the input light is transmitted, and the output light increases rapidly.

Once in the above state (d shown in Figures 3 and 4)
When the transition occurs, the nonlinear resistance element maintains a high resistance and a high voltage sharing state, and the quantum well maintains a non-absorbing state (transparent state). Therefore, even if the incident light decreases, the output light remains in a high output state (see Figures 3 and 4).
d) shown in the figure follows.

However, as the incident light further decreases, the load resistance in the quantum well increases and the shared voltage in the nonlinear resistance element decreases (down to c shown in Figures 3 and 4).
Then, the resistance of the nonlinear resistance element decreases rapidly, the current increases, and the voltage shared by the quantum well increases.
Therefore, the absorption characteristics of the quantum well shift from the solid line in FIG. 2 to the dotted line. Therefore, the quantum well now absorbs the incident light, and the output light is in a low power state (a shown in FIGS. 3 and 4).

FIG. 5 shows another embodiment of a semiconductor device using quantum wells according to the present invention, and is a diagram showing an example suitable for a nonlinear resistance element used in an optical bistable device.
FIG. 7 is a diagram for explaining the operation of a double barrier resonant tunnel diode, FIG. 7 is a diagram for explaining negative resistance characteristics, and FIG. 8 is a diagram showing an example of a triple barrier resonant tunnel diode with different spacing. , 11 indicates a barrier.

The example of a semiconductor device using quantum wells shown in FIG. 5 is one in which a non-linear resistance element is realized using the resonant tunneling effect in a plurality of quantum wells.
This is an example in which a resonant tunnel diode, which is a nonlinear resistance element, is constructed using a multi-quantum well structure in which a GaAs thin film and an AlGaAs thin film are stacked. Explaining the effect of this resonant tunnel diode using a double barrier, most of the light is initially reflected by the first barrier and a portion is transmitted, but it is also reflected by the second barrier. Now, as shown in Figure 6a and b, when the voltage is gradually increased and the current is caused to flow, the reflections occurring at the two locations cancel each other out and the current increases, and when the phases are completely weakened, The reflection becomes 0 and a large current _I1 flows. If the voltage is higher than that, the conditions for mutual cancellation break down and the current decreases rapidly.

Incidentally, in general, a nonlinear resistance element is required to have a large difference between the current I ₁ and the current I ₂ shown in FIG. However, if one more barrier with the above-mentioned effect is added to make the structure triple, the current I ₁ shown in FIG. 7 does not become very large because the resonance conditions in each barrier do not match. Therefore, a resonant tunneling diode simply made of triple barriers cannot provide a nonlinear resistance element with desirable characteristics.

Therefore, in order to increase the difference between the current I ₁ and the current I ₂ shown in FIG. 7 in a triple barrier resonant tunnel diode as shown in FIG. 5, the barrier spacing W ₁ shown in FIG. 8 must be increased. , W ₂ , for example, when the thickness of the barrier 11 is 23 Å, the interval W ₁ is 71 Å, and the interval W ₂ is 48 Å.
It is best to change it to something like Å. In other words, since electrons that have passed through the barrier are accelerated and their wavelength becomes shorter, we focused on this property and changed the interval W ₂ to the interval W ₁ accordingly.
Make it shorter. Usually, energy E = constant ×
Resonance occurs at (1/W) ₂ , so if the energy E is doubled when it passes through the first barrier, then the above-mentioned tube width W ₁ of 71 Å and interval W ₂ of 48 Å correspond to those conditions. Become.

When the triple barrier resonant tunneling diode as described above is used in the optical bistable device according to the present invention, MBE (Molecular Beam) is used as a GaAs-based multilayer thin film device.
It can be manufactured in an integrated manner using the epitaxy (molecular beam epitaxy) method. In this case, the triple-barrier resonant tunneling diode transmits light in contrast to the quantum well that controls light absorption/transmission, and of course requires adjustment of the material so that it does not depend on light. It is about. For this purpose, the absorption start wavelength may be made shorter than that of the light control layer. As an example, Al is added to each of the thin films shown in Figure 5, so that the GaAs layer becomes an Al _x Ga _1-x As layer, the AlGaAs layer becomes an Al _y Ga _1-y As layer, and The composition may be selected so as to satisfy the condition x<y.

Note that the present invention can be modified in various ways and is not limited to the above embodiments. For example, in the above embodiment, a quantum well with a multilayer film is used, but the quantum well does not need to be multilayer, and the incident direction of light may not be perpendicular to the film but may be horizontal. Further, the non-linear resistance element constituting the optical bistable element using quantum wells according to the present invention is not the triple barrier resonant tunnel diode explained with reference to FIGS. 5 to 8, but other elements may be used. good. Further, the non-linear resistance element may have an integrated structure with the light control layer as described above, but it may also be configured so that the light control layer and the electrical connection circuit can be connected without having an integrated structure. The composition of the multilayer film constituting the quantum well is GaAs as shown in the above example.
Needless to say, it may be something other than the system.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, it is only necessary to connect the quantum well and the nonlinear resistance element in series and apply a constant voltage, so the optical input/output relationship forms a hysteresis loop with a simple structure. An optical bistable device can be provided. Further, since the quantum well structure as described above is used, an optical bistable device can be manufactured by sequentially laminating a resonant tunnel diode and a light control layer on a semiconductor substrate. Therefore, it can be easily integrated and can be widely used as a semiconductor element for optical signal storage and logical operations.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining one embodiment of an optical bistable device using a quantum well of the present invention, Fig. 2 is a diagram showing the light absorption characteristics of a quantum well, and Fig. 3 is a diagram of a nonlinear resistance element. FIG. 4 is a diagram showing the input/output characteristics of an optically bistable device, and FIG. 5 is another example of a semiconductor device using a quantum well according to the present invention. A diagram showing a suitable example of a nonlinear resistance element used in the device, Figure 6 is a diagram to explain the operation of a double barrier resonant tunnel diode, and Figure 7 is a diagram to explain negative resistance characteristics. , FIG. 8 is a diagram showing an example of a triple barrier resonant tunnel diode with varying spacing. 1 is a power supply, 2, 3 and 11 are thin films, and 4 is a non-linear resistance element.

Claims (1)

[Claims] 1. A quantum well light control layer that is made of thin films with different compositions and whose light absorption characteristics shift from a high absorption coefficient to a low absorption coefficient in a specific wavelength range, and a nonlinear resistor that has negative resistance characteristics. Apply voltage with the element in series,
A semiconductor device using a quantum well, characterized in that the input/output characteristics of light in the above-mentioned specific wavelength range are controlled in a light control layer. 2. A semiconductor device using a quantum well according to claim 1, characterized in that a quantum well made of a multilayer film is used as a light control layer. 3. A semiconductor device using quantum wells, characterized in that a non-linear resistance element is realized by using a resonant tunneling effect in a plurality of quantum wells made of thin films of different compositions and having different film thicknesses.